Abstract
The relations between K, Ca and Mg contents of orchardgrass and the amount of these exchangeable elements in soil were investigated in spring on the mountainous sloping pastures where the surveys of previous report were carried out. The present report dealt with the countermeasures of fertilizer application on Mg content and K/(Ca+Mg) ratio of Orchardgrass for the prevention of grass tetany occurrence in relation to the soil cationic levels. 1. Since the highly significant positive correlation of K contents was obtained between soils and orchardgrass, it was estimated that the critical level of exchangeable soil K was about 13mg/100g dry soil assuming the critical K content of the herbage to be about 2%, and if the optimum K content of the herbage were 2-3%, the soil K might be 14-19mg. However, because of the ununiform distribution of soil K on the pasture, it was considered that the soil K should be 21-24mg to avoid partial K deficiency for the plant, where the K content of the herbage might be 3.2-3.6%. 2. The negative correlations were found between Mg content of orchardgrass and K and Ca levels in soils, however, the positive correlation of Mg contents was not found between the herbage and soils, possibly due to the high amount of soil Mg across the field. The significant correlations were not observed between Ca content of the herbage and any one of K, Ca and Mg levels in soils. 3. The Mg content of spring orchardgrass could be maintained at 0 2% or more which is considered as the safe level by KEMP, if the sufficient amount of magnesium and the proper amount of potassium fertilizer were applied to the pasture. 4. Although the increased Mg content in the herbage decreased the ratio of K/(Ca+Mg) considerably, it was also necessary to lower the K content of the herbage to ensure the ratio below 2.2 of the critical level indicated by KEMP and 'THart ; the soil K should be less than 20mg to maintain the ratio below 2.2. Under this condition, however, the K deficient orchardgrass will appear at more than 10% ratio in the pasture, because of the ununiform distribution of soil K. Consequently, only by orchardgrass, it is not possible to maintain the ratio lower than 2.2. Therefore, the establishment of mixed herbage with legume is necessary to maintain the good pasture in both the view-points of plant and animal nutrition.
